Due to the effect of wind loads on a bridge crane, for example, roll piles in a warehouse do not always become concentric with regard to all of the rolls. Due to damage to surface layers and other reasons, a varying number of web layers are removed from some of the rolls. Thus the diameter of rolls arriving in a warehouse, even rolls originating from the same trim-width roll set, may vary even tens of millimeters. Current up-enders do not centralize rolls in a roll set, but one side of the envelope surface of the rolls becomes substantially uniform with regard to the rolls in the roll set. The staggering caused by the diameter variation of the rolls accumulates on the opposite envelope surface. Thus the whole diameter variation becomes staggered on one side. In addition to the above, inaccuracies related to the operation of the crane also have an effect. As a combined effect of all these factors, the radial staggering of rolls piled in the warehouse may be several centimeters.
The compactness the matrix in which the piles can be positioned in a vertical roll warehouse has economic impact. Extra space between piles causes additional costs in terms of a broader extension of the bridge crane and a larger building surface area and reduces storage rate.
If it is necessary to include such structures in a gripper that extend below the roll/roll set during moving, the use of space becomes less efficient as more space must be reserved for the horizontal movement of the crane above the piles in the warehouse. Thus it is desirable to be able to ensure a safe hold during moving without having securing structures extending below the lowest roll.
Patent specification FR 2859197 discloses a secure solution per se for maintaining a safe hold of an object to be moved during the moving. The solution is suitable for a constant-sized drum, but less so for a paper roll, in which the location of the lower end may vary over a wide range, extending 0.3 to 4.5 m below the gripping mechanism. Scissor-type grippers are described on the website of Bushman Equipment Inc. at www.busman.com/prod_tgripper_broch.asp. The grippers in question are not suitable for handling vertical paper rolls. The grip is applied to a small surface area and damages at least the wrapper, possibly the roll as well.
Typically, scissor mechanisms provide the advantage of automatically increasing the gripping force when the weight of the load increases. Solutions are also disclosed in patent specifications DE 3822228 and U.S. Pat. No. 2,959,444. However, the mechanisms described represent solutions requiring a fairly large amount of space, and the compression force is not optimal over the whole diameter range. Patent specification FR 2699908 discloses a wedging mechanism that provides a grip at the upper end of a roll.
Thus it is common to known grippers compressing the envelope surface of the roll that they are unable to convey any significant compression force very far downwards. However, downward extension is a necessary feature in order to be able to transport roll sets of a plurality of rolls at the same time. If the mechanism providing the compression force on the gripper is located above the roll/roll pile and the compression force is moved 2.5 to 3 m downwards, this results in such massive structures that their application is not economically viable.
Known scissor-type solutions also operate in a very limited diameter range. They are not able to cover the range of 700 mm to 1,600 mm, typical of paper roll production. With paperboard rolls, the range may be even wider.